This invention relates to flexible high voltage gas-insulated cable, and more specifically relates to a novel soft insert pad disposed between a support insulator and the conductor supported thereby within the interior of the cable to prevent the generation of conductive particles within the housing of the cable.
Flexible gas-insulated cable structures for transmission and distribution of electric power at high voltage are well known and commonly consist of a central conductor supported within an outer housing which is filled with a dielectric gas such as sulfur hexafluoride under positive pressure. Both the outer housing and central conductor are corrugated or are otherwise made flexible to enable the reeling of the cable so that it can be shipped by truck or railroad car, and to enable the installation of the cable in an irregular terrain or ditch such that the cable will conform to the contours of the location in which it is installed.
The central conductor of the cable is frequently aluminum and the support insulators which support the central conductor within the outer sheath are usually a molded thermoplastic material such as an acrylic Plexiglass DR61K.
A preferred aluminum alloy, which is used for cable of this type, is a relatively soft high conductivity aluminum such as a 1100 aluminum alloy. The material of the support insulators is harder than the relatively soft aluminum so that during the manufacturing process and during the process of bending or reeling the assembled cable when there are axial stresses and possible movement between the central aluminum conductor and the plastic housing insulator, it is possible for the plastic insulator to gouge or abrade the outer surface of the soft aluminum, producing scractches on the aluminum surface and small chips of aluminum.
During operation, the aluminum particles, which are in an exceptionally high electric field since the small diameter cable might have a rated 330 kV or higher between the central conductor and outer housing, can cause breakdown of the dielectric gas and failure of the cable. Similarly, scratches in the aluminum surface can lead to corona discharge and ultimate failure of the cable.
Cables of the general type disclosed above are shown in numerous issued U.S. patents including U.S. Pat. No. 4,100,367 in the name of Netzel, U.S. Pat. No. 4,095,041 in the names of Netzel and Ponder, U.S. Pat. No. 4,101,730 in the name of Netzel, U.S. Pat. No. 4,122,298 in the name of Brandt.